Vascular Plants of Williamson County Daucus pusillus − RATTLESNAKE WEED [Apiaceae]

Daucus pusillus Michx., RATTLESNAKE WEED. Annual, taprooted, 1-stemmed at base, often unbranched below inflorescence, erect, in range 3–55 cm tall; shoots with feathery basal leaves and cauline leaves, basal leaves often absent at flowering, short-hirsute and somewhat bristly; when crushed scented like carrot. Stems: ± cylindric but slightly ridged with support tissue, aging smoother at base, to 2.5 mm diameter, with 5 or more ridges descending from each leaf alternating with minor veins, tough, young stem striped with green photosynthetic tissue and pinkish or reddish purple support tissue, having downward-arching hairs along reddish stripes; hollow. Leaves: helically alternate, odd- 2−3-pinnately compound and dissected, with to 6 symmetric pairs of lateral primary leaflets, petiolate and typically shortly fused around node forming a U-shaped sheath, without stipules; petiole sheath ± closed at base, deeply channeled, 4−75+ mm long, sheathing wings membranous, to 15 mm long, 0.3−0.7 mm wide at base, sometimes ciliate on margins, lower side ridged and short-hirsute; blade ± oblong to ovate in outline, to 75 mm long, blade ± = petiole; rachis channeled, somewhat 5-ridged on lower side, bristly short-hirsute; lateral primary leaflets ± opposite, pairs separated by < 16 mm along lower rachis decreasing upward; petiolules of primary leaflets 0−2.5 mm long; blades of primary leaflets ovate, to 20 mm long, divided into pinnately dissected or lobed secondary leaflets; petiolules of secondary leaflets deeply channeled, < 1 mm long; blade of secondary leaflets typically ovate, to 11 mm long, unlobed to several-lobed with alternate, deep sinuses, long- tapered at base, pinnately veined; ultimate lobes narrowly oblong or oblanceolate to elliptic or lanceolate, < 1−3 mm long, short-hirsute. Inflorescence: compound umbel, terminal and axillary, flat-topped or commonly depressed in center and appearing nestlike, 4−15(−25) mm across at first flowering, of 8−16+ umbellets, each umbellet 2−5 mm across, with (1−)2−10 bisexual flowers or of mostly bisexual flowers with 1−2 central staminate flowers, bracteate; bract subtending peduncle leaflike; peduncle erect, 10–170(– 250+) mm long increasing 2× in fruit, with ridges descending from the outer bracts of involucre, finely striped green and whitish, pubescent to short-hirsute; involucre of 5–8(– 11) bracts subtending outer primary rays in 1 whorl, bracts leaflike and petiolate, involucre bract petioles with membranous, whitish wings, ciliate on margins and surfaces hirsute, bract blade spreading, 1(−2)-pinnately lobed and ovate in outline, 7.5–15 × 3.5–10 mm increasing 2× in fruit and often conspicuous with the longest bracts > outer fruits, ciliate on margins, puberulent on lower surface; primary rays ascending, unequal with the shortest ray in center, cylindric, at anthesis 1–3 mm long increasing 2× in fruit, green, short hirsute- hispid; involucel of 3−6 bractlets subtending outer pedicels, bractlets whorled, ascending or appressed (at anthesis), unequal and dimorphic, the involucel of an outer umbellet typically with 2 long bractlets separated by a shorter bractlet on outer side and 3 short bractlets on inner side, involucel of an intermediate umbellet with only 1 long bractlet on outer side, involucel of the innermost umbellets with only short bractlets; long bractlets linear to lanceolate, 3.5–5 mm long, greenish with membranous wing at base, ciliate on margins, lower surface hirsute, short bractlets ovate to deltate or oblong, < 1.5 mm long, membranous, ciliate on margins; pedicel 0.5−1.5(–3) mm long increasing in fruit, outer pedicels > central pedicel, green, faintly ridged. Staminate flower: radial, small; sepals absent; petals 5, permanently incurved with acuminate tip fused with midridge on upper (inner) surface, appearing roundish-cordate and slightly saclike on each side of midvein, ca. 0.3 mm long, white; stamens 5, free; filaments ca. 0.25 mm long, light yellowish green, initially erect and hooked inward at tip but at anthesis becoming straight and spreading out between petals; anthers dorsifixed, dithecal, heart-shaped, 0.2 mm long, light yellow, longitudinally dehiscent; pollen pale amber; pistil 1 but diminutive and less bristly than in bisexual flower, mostly a 2-lobed, nectar-producing platform (stylopodium, stylar tissue). Bisexual flower: radial, small; sepals absent; petals 5, permanently incurved with acuminate tip fused with midridge on upper (inner) surface, appearing roundish- cordate and slightly saclike on each side of midvein, ca. 0.3 mm long, white becoming purplish red (except remaining white on some central flowers); stamens 5, free; filaments ca. 0.25 mm long, light yellowish green, initially erect and hooked inward at tip but at anthesis becoming straight and spreading out between petals; anthers dorsifixed, dithecal, heart-shaped, 0.15−0.2 mm long and wide, whitish, longitudinally dehiscent; pollen whitish; pistil 1; ovary inferior with 2-lobed, nectar-producing platform (stylopodium, stylar tissue) on top, compressed-oblong, 0.5–1 × 0.4–0.7 mm, green, 10-ribbed, the ribs bearing radiating white bristles, 2-chambered, each chamber with 1 ovule; styles 2, ascending, < 0.2 mm long, light green; stigma minutely capitate, yellowish green, papillate. Fruit: schizocarp, of 2 dry, 1-seeded halves (mericarps), mericarps hemi- ellipsoid, 2–2.5 × 0.8–1.1 mm (excluding bristles and prickles), concave or flattish on inner face, slightly beaked (persistent style), with radiating bristles from the original 5 ribs of ovary and prickles from secondarily formed ribs between original ribs, the bristles 0.2–0.6 mm long, whitish, the prickles much larger than bristles, 0.5–1.2 mm long, purplish becoming brown or aging tan, flattish and ± continuous (confluent) at base, barbed at the tip. A. C. Gibson & B. A. Prigge